形状记忆合金简介

•形状记忆效应：具有一定形状的固体材料(通常是具有热弹性马氏体相变的材料)，在某一温度下(处于马氏体状态M f 进行一定限度的塑性变形后，通过加热到某一温度(通常是该材料马氏体完全消失温度A f )上时，材料恢复到变形前的初板条马氏体
钢的淬火
5
•Monoclinic Crystal Structure
Twinned Martensite 自协作马氏体Detwinned Martensite
非自协作马氏体
8
发生塑性变形后，经加热到
某一温度后能够恢复变形，
马氏体在外力下变形成某一
特定形状，加热时已发生形
变的马氏体会回到原来奥氏
形状记忆效应过
程的示意图
马氏体相变热力学
相变产生，M相的化学自由能必须
，不过冷到适当低于T0(A相和M相化学自由
的温度，相变不能进行，
必须过热到适当高于T0的温度，相变才
马氏体相和母相化学自
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马氏体相变热力学
低于M
s
温度下，马氏体形成以后，界面上的弹性变形随着马氏体的长大而增加；
当表面能、弹性变形能及共格界面能等能量消耗的增加与变化学自由能的减少相等时，马氏体和母相间达到热弹性平衡状态，马氏体停止长大。

CuAlNi合金加热过程中热弹性马氏体相变(马氏体缩小)温度继续下降，马氏体相变驱动力增加，马氏体又继续长大，也可能出现新的马氏体生长。

温度升高，相变驱动力减小，马氏体出现收缩。

CuAlNi合金加热过程中热弹性马氏体相变(马氏体缩小)
16伪弹性应力应变示意图
17f
(a) Shape Memory Effect (b) Superelasticity
[100][111]
冷却
形状记忆效应的三种形式
(a)单程(b)双程(c)全程
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（a）马氏体状态下未变形
（b）马氏体状态下已变形
）放入热水中，高温下恢复奥氏体状态，形状完全恢复
单程TiNi记忆合金弹簧的动作变化情况
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没放入热水前放入热水后冷却至室温后再次放入热水后
双程CuZnAl记忆合金花的动作变化情况
TiNi合金的全程记忆效应（100℃-室温）
TiNi合金的全程记忆效应（低温-100℃）
铁磁性形状记忆合金简介
温控形状记忆
铁磁性
铁磁性形状记
兼有磁致伸缩材料和传统温控形状记忆材料的优点
响应频率快磁致应变大
The magnetic easy axis changes from one twin to the other
•Weak magnetic anisotropy.
Effect of a magnetic field
Weak anisotropy Strong anisotropy
In systems with strong anisotropy and highly mobile boundaries, field induced
et al. J.Appl.Phys. 92,3867 (2002);
Moya et al. Phys. Rev. B 73, 64303 (2006); 74, 24109 (2006).)
33
(1) Via martensite variant reorientation-Ni2MnGa
(2) Via magnetic field induced martensitic
transformation-NiMnIn(Sn,Sb)
37
Ni 2MnGa -crystal structure
Ni 2MnGa is the most successful magnetic shape memory alloy. It transforms from the Heusler cubic structure to tetragonal on cooling. A 6% magnetic field induced tensile strain has
been recorded in a single crystal, by the mechanism of martensite variant reorientation.
The absence of a thermal effect makes it suitable for high frequency operations. The mechanical work output, however, is much
lower than those of thermal SMAs .
ΔV= -1.30%:
The volume change is large. The material is an intermetallic compound and is intrinsically brittle Îtransformation induced cracking . The problem is much less severe with single crystals.
Tetragonal Martensite
Cubic Austenite
-4.45%
1.63%
a
a
c a
a
a
[100]c expansion by 1.63%[001]c contraction by –4.45%The tetragonal structure is mechanically anisotropic. The
maximum linear strain is when axis [001] is converted to [100]: ~6%
Mn Ni
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c c
(110)c plane of A
c
c
Ni 2MnGa –structural anisotropy of M
(110)c T w i n p l a n e
[100]c projection plane of A [100]c projection plane of M
Marioni , JMMM, 290-291 (2005) 35
Now we have got a working mechanism for shape change
39Ni 2MnGa –magnetic anisotropy
(110)c
[001]c
(the c -axis of M)
[001]c
(the c -axis of M)
Structure anisotropy Magnetic anisotropy
The tetragonal structure is a uniaxial structure magnetically. Its c -axis is the
easy direction of magnetization
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Li et al, APL, 84, 3594 (2004).
Ni 2MnGa –magnetic anisotropy
Wu et al: APL. 75, 2990 (1999).
Martensite
Austenite
[001]
-3-23
01
5.8x10J/g=4.5x10J/cm 2
E H M μΔ=Δ=For a phase transformation at room temperature, the T ΔS energy is typically
~80 J/cm 3The driving force is too small to induce austenite -martensite transformation
Co 2NiGa
Ni 2MnGa
41Possibility of magnetic field
induced deformation via
martensite reorientation
Magnetization curves along easy ([001]) and hard
([100]) axes of Ni 48Mn 30Ga 22constrained in single variant martensite. The magnetic driving force (energy) is ~0.08 J/cm 3. Likhachev: Phys. Lett. A 275 (2000) 142.
Ni 2MnGa deformed along [100] direction at 300 K in martensitic state. Chernenko et al: Phys. Rev.
B 69134410 (2004)The mechanical resistive force is ~1.5 MPa and the mechanical frictional energy is 0.09 J/cm 3
Ni 2MnGa –magnetic anisotropy
c
a
a
c
42
Heczko et al. JMMM 226-230 (2001) 996
NiMnGa
43Heczko et al. JMMM 242–245 (2002) 1446
Ni 2MnGa –magnetic field induced martensite reorientation
6% strain is induced by
magnetic field via martensite reorientation. The strain is irreversible.
NiMnGa
Ferromagnetic martensite/austenite
paramagnetic austenite/martensite
47TiNi 形状记忆合金的应力应变曲线。